1. Field of the Invention
The present invention relates to one used in a high-pressure fuel passage connecting between a high-pressure fuel pump and a fuel rail in a fuel supplying apparatus for a direct injection engine, and more specifically relates to a terminal structure of a high-pressure fuel pipe for a direct injection engine where a connection head is brazed to an end of a fuel pipe composed of a steel pipe or a stainless steel pipe.
2. Description of the Related Art
As a conventional terminal structure of a high-pressure fuel pipe for a direct injection engine, there is generally one where a connection head having a spherical or a curved-face pressing seat face and a fuel pipe insertion portion positioned on the opposite side of the pressing seat face is brazed to an end of a fuel pipe composed of a steel pipe or a stainless steel pipe.
FIG. 5 shows an example of the terminal structure of a high-pressure fuel pipe for a direct injection engine, and one where a connection head 22 having a spherical or a curved-face pressing seat face 22-1 at a distal end thereof and a fuel pipe insertion portion 22-2 (generally called “hakama (skirt)” in Japan) for securing a brazing area on the opposite side of the pressing seat face has been brazed to an end of a fuel pipe 21 composed of a steel pipe or a stainless pipe is known (see DE 10 2005 045 731 A1). That is, such a terminal structure of a high-pressure fuel pipe for a direct injection engine is configured by fitting the fuel pipe insertion portion 22-2 of the connection head 22 having a spherical or a curved-face pressing seat face 22-1 at a distal end thereof and the fuel pipe insertion portion 22-2 formed on the opposite side of the pressing seat face to a straight pipe portion at the end of the fuel pipe 21 composed of a steel pipe or a stainless steel pipe and brazing the fitted portion.
Further, FIG. 6 shows an example of a terminal structure of an eye joint used for a high-pressure fuel pipe for a direct injection engine, where an eye joint main body (corresponding to the above “connection head”) 24 having an annular recessed groove 24-1 internally, having a wall portion 24-2 positioned on the side of a circumferential side of the annular recessed groove 24-1 and bulged in an arc shape, having a connection hole 24-3 communicating with the annular recessed groove 24-1 and a mounting hole 24-4 bored at an axial core portion, and having a short cylindrical wall (corresponding to the above “hakama”) 24-5 formed by integrally protruding a hole peripheral wall of the connection hole 24-3 outward and having an inner diameter smaller than a diameter of the fuel pipe 23 has been brazed to an end of a fuel pipe 23 composed of a steel pipe or a stainless steel pipe, and this eye joint is configured by performing one-stage drawing work to the connection end of the fuel pipe 23, fitting the drawn portion into the short cylindrical wall 24-5 of the eye joint main body and brazing the fitted portion (see Japanese Patent Application Laid-Open No. H1992-347091).
However, such conventional terminal structures of a high-pressure fuel pipe for a direct injection engine and of the eye joint used for a high-pressure fuel pipe for a direct injection engine have the following problems described below.
In the case of the terminal structure of a high-pressure fuel pipe for a direct injection engine shown in FIG. 5, by providing the fuel pipe insertion portion (hakama) 22-2 for securing a brazing area on the opposite side of the pressing seat face 22-1 of the connection head 22, such an effect that enables to secure a sufficient brazing area and thereby a brazing strength to the connection head 22 to improve can be achieved; however, since the straight pipe portion of the end of the fuel pipe 21 is fitted to the fuel pipe insertion portion (hakama) 22-2 of the connection head 22 to be brazed, a thinner pipe must be adopted as the fuel pipe 21, which results in such a problem that an inner volume cannot be secured sufficiently and requirements cannot be satisfied regarding such a performance aspect as pulsation or pressure loss.
Further, in the terminal structure of an eye joint used for a high-pressure fuel pipe for a direct injection engine shown in FIG. 6, since the eye joint is configured by performing one-stage drawing work to the straight pipe portion at the end of the fuel pipe 23 to reduce a diameter of the straight pipe portion, fitting the reduced-diameter pipe portion into the short cylindrical wall 24-5 of the eye joint main body 24, and brazing the fitted portion, there is such a problem that stress is concentrated to the drawn portion of the terminal portion of the fuel pipe 23 in the vicinity of the short cylindrical wall 24-5 and a possibility that the fuel pipe 23 is broken from the drawn portion becomes large.
The present invention has been made in order to solve such conventional problems, and an object thereof is to propose a terminal structure of a high-pressure fuel pipe for a direct injection engine which not only can improve the brazing strength to the connection head but also can prevent stress concentration to the brazed portion with the connection head effectively even if a thin-diameter pipe is adopted as the fuel pipe and drawing work has been applied to an end of the pipe in view of the problem of pulsation or an internal volume, the performance aspect, or the like.